Developing method and device therefor for use in wet type electronic or electrostatic photography

ABSTRACT

A DEVELOPING METHOD AND DEVICE THEREFOR FOR USE IN WET TYPE ELECTROSTATIC PHOTOGRAPHY WHEREIN THE POLARITIES OF DC VOLTAGE APPLED TO A PAIR OF BIAS ELECTRODES ARE REVERSED. ACCUMULATION OF DEVELOPING TONER TO THE ELECTRODES CAN BE PREVENTED.

July 25, 1972 NOBUIYUKI KATAGIRJ ETAL 3,679,453

DEVELOPING METHOD AND DEVICE THEREFOR FOR USE IN WET TYPE ELECTRONIC OR ELECTROSTATIC PHOTOGRAPHY Filed March 21, 1969 FIG. 2

INVENTOR S NOBUYL/Kl KATAGJRI HI DEAKI Am YA MA ATTORNE Y S United States Patent Office 3,679,453 Patented July 25, 1972 Int. Cl. G03g 13/10, /10

US. Cl. 117-37 LE 8 Claims ABSTRACT OF THE DISCLOSURE A developing method and device therefor for use in wet type electrostatic photography wherein the polarities of DC voltage applied to a pair of bias electrodes are reversed. Accumulation of developing toner to the electrodes can be prevented.

BACKGROUND OF THE INVENTION The present invention relates to a developing method and a device therefor for use in a wet type electronic or electrostatic photography, and more particularly to an improved developing method and a device therefor for use in a wet type electronic or electrostatic photography of the type in which a pair of electrodes are electrically biased during the developing process.

There has been utilized in the prior art the so-called bias-developing method in which a pair of electrodes are disposed on the opposite sides of an exposed sensitized sheet material to be developed and DC voltage is applied across this pair of electrodes. In this case, when the polarities of the electrodes remain unchanged, the toner is attracted to that one of the pair of electrodes having the opposite polarity, and accumulated, so that the concentration of the developing solution is subjected to variation to such an extent that the developing solution reduces its function of reducing the edge effect of the image by the bias-developing method and stains the image.

The primary object of the present invention is there fore to eliminate the defects of the conventional method of the type described.

SUMMARY OF THE INVENTION In brief, the method of the present invention is to reverse the polarities of a pair of electrodes used for the bias-developing method. Therefore, the toner accumulated on one of the electrodes is released therefrom upon reversing the polarities and is dispersed into the developing solution.

In one embodiment of the present invention, a pair of bias electrodes are held in stationary position while their polarities are reversed by reversing the polarities of a DC voltage applied to the electrodes by a power circuit switching device.

In another embodiment of the present invention, the polarities of the DC voltage remain unchanged at the output terminals of the power circuit, but the positions of the electrodes are rotated, thereby reversing their polarities. In this case, since electrodes each having a large surface area are required when only one pair of electrodes are used, the space for installation and rotation of these electrodes becomes inevitably larger. According to the present invention, one electrode is divided into a plurality of elongated electrodes. A plurality of pairs of such elongated electrodes are disposed and rotated for reversing the polarities, whereby the space needs not to be enlarged much larger than the space for the stationary electrodes.

The above and other objects, features and advantages of the present invention will become more apparent from the following description in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a partially sectional view of one embodiment of a wet type electronic or electrostatic photographic developing device; and

FIG. 2 is a perspective view of another embodiment of a pair of electrodes and its associated electricity feeding mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT A pair of bias voltage electrodes 1 and 2 are disposed within a developing chamber 3 and a sensitized sheet material 4 is interposed between the pair of electrodes in spaced apart relation therewith by a suitable distance. The above pair of electrodes 1 and 2, the developing chamber 3 and the sensitized sheet material 4 are all immersed in developing solution 5 in which are dispersed toner with either positive or negative polarity. Lead wires 6 are connected to a suitable power source (not shown) and apply a DC voltage across the pair of electrodes through a circuit switching device 6a suificient for producing a clear image upon the sensitized sheet material 4.

When the switching device 6a is switched to the right hand contacts in FIG. 1, so that a negative polarity is ap plied to the electrode 1 and a positive polarity is applied to the electrode 2, toner tends to adhere to and accumuate on either of the electrodes 1 or 2 having a polarity opposite to that of the toner. Therefore, when the switching device 6a is switched to the left hand contacts at a suitable time, so that the polarities of the pair of electrodes 1 and 2 are reversed, the toner accumulated on one of the electrodes is released or repelled from said one electrode, dispersing into the developing solution and finally no toner is adhered to said one electrode. However, toner starts to adhere and accumulate on the other electrode. Then, after a suitable time, the polarities of the pair of electrodes are reversed again. This process is cycled.

However, when the pair of electrodes 1 and 2 are held stationarily, as described hereinabove, while their polarities are reversed, it is necessary that the sensitized sheet materials must be turned upside down every time that the polarities are reversed, causing a tedious developing operation. In order to eliminate such defect, the positions of the pair of electrodes are reversed while the direction of the electric field established therebetween remains unchanged, as will be described in more detail hereinafter.

FIG. 2 shows one embodiment of a pair of electrodes which are rotated to reverse their polarities. A pair of electrodes 11 and 12 are integrally disposed in spaced apart relation at a suitable distance by means of end plates 13 and 13a. Suitable shafts 14 and 14a extend from the end plates 13 and 13a, respectively. The shaft 14a carries a toothed wheel 15 which is in mesh with a gear drivingly coupled to a drive means (neither of which are shown). Feed segments 16 and 17 are attached to the shaft 14 through a suitable electrical insulating material in spaced apart relation with each other. Each segment is electrically coupled to its associated electrode. Brushes 18 and 19 are so disposed as to be in contact with the segments 16 and 17, respectively. An exposed sensitized sheet having an electrostatic pattern thereupon is developed when it is fed through the pair of electrodes 11 and 12.

In order to reverse the polarities imparted to the pair of electrodes 11 and 12, they are rotated through the toothed wheel 15, or manually, so that the positions of the pair of electrodes 11 and 12 are reversed.

It is preferable that the surface area of each electrode is slightly larger than that of the sensitized sheet. But when the pair of electrodes have large surface areas, their installation space will be inevitably increased, thereby increasing the dimensions of the processing device. To eliminate this defect, a plurality of pairs of elongated electrodes, of the type shown in FIG. 2, may be disposed in the juxtaposed relation so that the total area of these electrodes may become larger than that of the sensitized sheet. In this construction, the polarities of the electrodes can be easily reversed by the rotation of each pair of electrodes which are elongated and require less installation or assembly space.

In the embodiments described hereinabove, the pair of electrodes have been shown as being in the form of plates, but it will be understood that the invention is not limited thereto, and electrodes in other forms such as rollers, may be used.

Next, a few examples of the present invention will be described.

EXAMPLE 1 A light sensitized sheet having a photoconduotive layer comprising zinc oxide dispersed in resin was electrically charged with negative polarity by means of corona discharge with a potential of 5 kv. for a few seconds spaced apart from the sheet by a distance of '12 mm. Thereafter, the original was superposed thereupon and the sheet was exposed for one second by a tungsten lamp of 100 luxes, thereby forming an electrostatic latent image thereupon. The sheet was fed into the developing chamber, as shown in FIG. 1, for developing. The developing toner in the chamber was commercially obtained and electrically charged with positive polarity. The electrodes were spaced apart from each other by a distance of 5 mm. with an applied DC voltage of 30 v. and a developing time of 3 sec. The polarities of the electrodes were then reversed by switching the switching device (designated by 6a in FIG. 1), and after a few seconds the sheet was removed and the polarities were reversed again to the original polarities. In a similar manner, tens of sheets were developed, successively. Thereafter, the polarities were reversed and maintained during washing operation of the electrodes. The electrodes were taken out of the chamber, but no stain thereof due to toner attachment was observed.

For the sake of comparison, the electrodes were taken out just only after one developing without the above washing, and the stain thereof was remarkably increased as compared with the above electrodes Washed by reversing the polarities.

EXAMPLE 2 The same light sensitized sheet as that described in Example 1 was electrically charged at a negative polarity for 30 see. by corona discharge of -5 kv. and spaced apart from the sheet by '15 cm. The original superposed upon the charged sheet and the sheet was exposed for sec. by a tungsten lamp of 60 lux, thereby producing an electrostatic latent image. The exposed sheet was fed into a developing chamber in which were disposed five pairs of electrodes of the type shown in FIG. 2, in juxtaposed relation. The total surface area of these electrodes was in excess of the surface area of the sheet by about 10%. The developing conditions are: 3 mm. between a pair of electrodes; DC voltage applied to brushes, v.; and developing time, 60 sec. Toner was obtained in the market, but particle size was finer than that of the toner used in Example 1.

'Each of the toothed wheels coupled to each pair of electrodes were rotated through 180 after every developing. In this manner, tens of sheets were developed and thereafter, the electrodes were taken out of the developing chamber. No stain due to toner was observed.

The invention has been described so far with particular reference to the embodiments thereof, but it will be understood that variations and modifications can be effected without departing from the spirit of the invention as described hereinafter and as defined in the appended claims. We claim: 1. A bias developing method in wet electronic or electrostatic photography, comprising the steps of immersing a sensitized sheet material having an electrostatic latent image on one side in a liquid developer having toner particles of a specific electrical polarity charge; developing the sheet material by producing an electric field through said liquid developer around the sheet material by applying a DC voltage to a pair of electrodes having terminals and located on both sides of the sheet material with a positive polarity at one electrode and a negative polarity at the other electrode one of said terminals having one of said polarities facing said one side of the sheet material; reversing the; polarity of the DC voltage at each of the electrodes so that toner particles attracted to that electrode having a polarity opposite the polarity of the toner particles during the development of the sheet material are released from such electrode, and maintaining said one side of the sheet material facing said one polarity when the polarities are reversed.

2. A bias developing method as set forth in claim 1 further comprising the step of turning said sheet material upside down when the polarities are reversed to maintain said one side of the sheet material facing said one polarity.

3. A bias developing material as set forth in claim 1 further comprising the step of reversing the positions of said terminals when said polarities are reversed to maintain said one side of the sheet material facing said one polarity.

4. A bias developing device for wet electronic or electronstatic photography, comprising a container having a liquid developer therein having toner particles of a specific electrical polarity charge;

a sensitized sheet material having an electrostatic latent image on one side thereof immersed in the liquid developer;

a pair of electrodes having terminals, one on each side of the sheet material in the developer;

electrical power means connected to the electrodes for producing an electric field around the sheet material by applying a DC voltage to the electrodes with a positive polarity at one electrode and a negative polarity at the other electrodes one of said polarities being carried on one of said terminals facing said one side, and for reversing the polarity of the DC voltage at each of the electrodes so that toner particles attracted to the electrode having a polarity opposite the polarity of the toner particles during the development of the sheet material are released from such electrode, and

means for maintaining said one side of said sheet material facing said one polarity when said polarities are reversed.

5. A bias developing device as claimed in claim 4, wherein the electrical power means comprises a DC voltage source having 'positive and negative polarity terminals and a double-pole, double-throw switch having each of one pair of terminals connected to a corresponding one of the terminals of the DC voltage source and each of another pair of terminals connected to a corresponding one of the electrodes.

the positions of said electrodes when said polarities are reversed.

7. A bias developing device as claimed in claim 6, wherein the electrical power means and the means for maintaining comprise rotatable mounting means having a shaft and supporting the electrodes for rotation about the shaft, drive means coupled to the mounting means for rotating said mounting means, a pair of feed segments mounted on the shaft and electrically insulated from each other each connected to a corresponding one of the electrodes, an electrical voltage source having a pair of terminals, and a pair of brushes each connected to a corresponding one of the terminals of the electrical voltage source and each in electrical contact with a different one of the feed segments.

8. A bias developing device as claimed in claim 7, wherein each of the electrodes comprises a plurality of electrodes mounted in juxtaposed relation on the mounting means.

References Cited UNITED STATES PATENTS Crumrine et a1 118-637 Metcalfe et a1 117-37 X Kaprelian 117-37 X Greig 117-175 Matkam et a1 117-37 X Kollsman 204-180 Clark et a1 117-37 X Fauser et a1. 118-637 X Waterman et a1. 204-302 Matkovich 118-637 X 5 MURRAY KATZ, Primary Examiner M. SOFECLEOUS, Assistant Examiner US. Cl. X.R.

96-1 LY; 118-637, DIG 23; 204-181 

